Mobile telephones communicate wirelessly with an unmovable system comprising base stations. The base stations, BS, are arranged so that each BS covers a cell area and the cells are arranged so that they cover a complete area, where service should be provided. The covered area is aimed to be continuous so that the user equipment, UE, can move within the area without losing connection to a BS. When the UE moves from one cell area to another, communication moves from one BS to another BS in the new cell area.
The UE maintains information about BSs and cells in the neighborhood by scanning the radio channels. Each BS may broadcast a pilot signal and the UE determines if the signal strength is sufficiently large for communication according to any criterion.
The UE is normally operated by batteries having a limited capacity and scanning for neighboring BSs consumes such battery power. Thus, there is a tradeoff between how often a search should be performed for updating the BS information in the UE and the standby time of the UE between battery charging (or exchange thereof).
EP 1 463 347 discloses a method of network acquisition in which information about the cell, which was camped on when the UE was switched off, is stored in a memory of the UE. When the UE is switched on, it is likely that it is switched on at a place within the coverage of a cell in which it was previously switched off. By initially scanning the cells stored in the memory, the UE will often obtain cell camping faster. If only a small number, such as 20, of such cells, in which the UE has been switched off, is stored, the initial scanning will be fast. If no coverage is found, a complete scan is performed. If the UE loses coverage, information on that cell is also stored as if the UE was switched off.